A. Field of the Invention
The present invention relates to the field of adjustable counterbalanced stands for supporting a load, more specifically a surgical microscope, to be selectively positioned by a user.
B. Description of the Prior Art
Surgical microscopes are being used more and more in surgery. Because of their heavy weight, they must be supported on stands. Several noted manufacturers have offered stands which meet the requirement of holding the load of the surgical microscope from the mechanical and static viewpoint. The applicant, for instance, sells stands with the designation OH, which are produced by Mitaka and other manufacturers. One example of such a stand appears in European Patent Application A-628 290. Zeiss, for example, disclosed a stand in European Patent 47 65 52. Most of the modern stands have parallelogram supports so as to be able to support the load of the surgical microscope without bending or twisting, so that the microscope will have the maximum freedom of movement and maximum radius of action.
European Patent Application A-628 290, for example, shows such a design. The design shown in FIG. 1 of that patent has a massive C-shaped base pedestal which carries a first parallelogram support, extended vertically and pivotable about a vertical pivot axis. The first parallelogram support carries a second parallelogram support extending horizontally, which can be pivoted about a first horizontal pivot axis. A connection between the two parallelogram supports with an additional pivot point on the base pedestal keeps both the vertical arms of the second parallelogram support always in the vertical position.
On the peripheral vertical arm of the second parallelogram support there is a third parallelogram support, extended horizontally, pivotable about a second horizontal pivot axis. Its peripheral vertical arm is likewise always held vertical and is connected, as a single piece, with a central vertical arm of a fourth parallelogram support which extends vertically.
A surgical microscope is mounted, so that it can be rotated or pivoted, on a lower horizontal arm of the fourth parallelogram support. With this mounting it has any desired degree of freedom so that it can be moved to a desired position by the user and held in that position. All of the parallelogram supports have relatively massive main supports and weaker secondary supports which transfer essentially only tensions or pressures. For static reasons it turns out that all the massive main supports are turned toward the space circumscribed by the stand, which is usually utilized by the user.
The main supports are bent out of their linear longitudinal extension, which is statically effective, by right-angle joints. That was desired at the state of the technology, because that was how designers attempted to keep the user's space as great as possible.
One of the ideas of the standard surgical stand manufacturers was that very massive parts and heavier counterweights improved the stability of the stand during its use.
The Contraves company also offered a similar microscope stand with two separate counterweights. One is movable in the horizontal direction on a horizontal parallel bar which transfers the balancing force, and the other is movable in the vertical direction. Such a stand is described, for instance, in the older European Patent Application B 476 551. That stand avoided right-angle joints. That caused a certain limitation of the working space for the user, as can be seen by comparing, for instance, FIG. 1 of the '551 publication with FIG. 4 of the '290 publication.
A stand according to the more recent Europe an Patent Application A-628 290 was marketed by its applicant (Mitaka) along with this applicant. That stand's advantage of gaining space was combined with disadvantages, though.
Production of the bent arms is considerably more expensive than use of straight arms. The bends in the main support produce shear-like overlaps with the secondary s upports at the ends of the parallel supports. That is best seen from FIGS. 1-6 of the European Patent Application. The se overlaps conceal a certain disadvantage, especially for inexperienced operating personnel, because if the personnel are not careful, cables, items of clothing, objects, or even arms or legs can get caught. That is particularly true for the region immediately around the load , e.g., the microscope, as that is where the user generally does most of his direct work.